Florence Rena Sabin was born November 9, 1871, in Central City, Colorado, the youngest of two daughters of Serena Miner and George K. Sabin. Her father was a mining engineer and she spent her early years in mining communities. Serena Sabin died when Florence was seven and she and her sister, Mary, lived with relatives in Chicago and Vermont. Sabin graduated from Smith College in 1893. In order to earn money for medical school, she taught mathematics in Denver for two years and was an assistant in the Zoology Department at Smith College from 1895 to1896. She entered Johns Hopkins Medical School in 1896 as a member of the fourth class to admit women. Upon graduation she was awarded an internship with renowned teacher and physician Sir William Osler at Johns Hopkins Hospital. Under the direction of embryologist and head of the Department of Anatomy, Franklin P. Mall, she undertook a project which led to the construction of a three-dimensional model of the mid and lower brain. It was adapted for publication in 1901.

After completing her internship in 1901, Sabin continued her anatomical and histological research with the help of a fellowship from a group of Baltimore women who aided women's education. In 1902, she became assistant in the department of anatomy, the first woman on the Hopkins medical faculty. She rose to full professor in 1917, the first woman at the university to achieve that rank. Sabin spent twenty-five years at Hopkins and during her early years there she concentrated her research mainly upon the origins of blood cells and the lymphatic system. She wrote a number of widely cited papers based upon her work. Sabin had many devoted students, many of whom followed scientific careers, and a number of them became leaders in the fields of anatomy, immunology, and hematology. In 1925, she became the first woman elected to membership in the National Academy of Sciences. She also was the first woman to receive full membership at the Rockefeller Institute in New York. At the institute she worked for thirteen years as head of a section that studied the cellular aspects of immunity.

Sabin retired to Colorado in 1938 to live with her sister Mary. She remained professionally active and carried on an extensive correspondence with her former students and colleagues. In 1944, she was asked by Colorado governor John Vivian to serve on his post-war planning committee which was organized to assess public health needs in the state. She did research, traveled, spoke, and wrote extensively. She lobbied colleagues, legislators and state officials to support a reorganized and better-financed public health program and worked for successful passage of a series of health laws drafted by her committee and known as the Sabin program. In 1947 she was appointed chair of the Interim Board of Health and Hospitals of Denver, a post she held until 1951. Sabin received many honors and awards. Buildings were named for her at the University of Colorado School of Medicine and at Smith College. She is one of two Coloradoans and one of a handful of women represented by statues in the United States Capitol. Sabin died October 3, 1953, in Denver of a heart attack.